Various methods are available for this purpose. The antenna far field pattern can be determined for example by means of a far field measurement. In practice, however, such a far field measurement is not very practicable, since it would be disrupted by many other devices. A further possibility lies in the use of a compact range chamber, and a plane wave can be generated for the measurement by means of a feedhorn and a mirror. However, such a structure may be very large in terms of the dimensions and the measurement chamber as a whole may be very expensive, so that such a method is also not very practicable in practice.
Therefore a near field measurement is predominantly carried out because it functions with relatively small chamber sizes. If shielded measurement chambers are used, then the measurements can be carried out completely independently of external RF services and interference sources. With such a near field measurement the antenna to be examined is measured in the measurement chamber. If both the magnitude and also the phase are captured over the entire solid angle or over selected ranges, the required antenna far field pattern can be mathematically determined therefrom. This takes place by means of a near field/far field transformation.
However, such near field measurement is problematic in the case of active antenna systems (AAS) in which the RF connection between antenna and radio is not usually accessible. Here the necessary data must be extracted or fed in at the usual digital interface. Normally only the power of the transmission or reception signal is available at this interface. On the other hand, the phase information can only be extracted with great difficulty or not at all. For this purpose a collaboration with the manufacturer of the active antenna system is generally necessary. Without phase information, however, the near field/far field transformation cannot be carried out.
However, in the case of an active antenna system the combination of antenna and radio electronics is measured. In this case the transmission direction and the reception direction must be measured separately because they relate to different electronic components.
Within the standardization committee of 3GPP this problem has already been discussed under R4-145044, “Near Field Measurement Setups for AAS BS OTA testing: 3GPP TSG-RAN4-Meeting #72”. A method was proposed there in which a reference antenna together with the active antenna system to be examined is moved by a rotary arrangement, so that different solid angles can be set in relation to a transmitting antenna. If the active antenna system acts as a transmitter, the required phase information can be determined by direct comparison of the phases of the RF signals from the reference antenna and the transmitting antenna which in this case acts as a receiver.
However, the problem of how to proceed in the reception direction, i.e. if the active antenna system functions as a receiver, is not solved. Moreover, a further problem is how to ensure, during the entire duration of the measurement over all solid angles, that the phase is not delayed, which is not ensured because of temperature drifts of the electronics of the active antenna system. In addition a synchronization between the separate transmitter and the receiver of the active antenna system would be necessary.
Therefore the object of the invention is to create a method and a measuring arrangement by which it is possible to determine the magnitude and the phase of an active antenna system, wherein the active antenna system functions as a receiver.
With regard to the method for determining the power values of a signal received by the active antenna in order thus to be able to determine the magnitude and the phase, the object is achieved by the features of claim 1. With regard to the measuring device for determining the power values of a signal received by the active antenna for calculation of the magnitude and the phase, the object is achieved by the features of claim 13. Advantageous modifications of the method according to the invention, as well as the measuring device according to the invention, are specified in the respective subordinate claims.
The method according to the invention for determining the power values of a signal received by the active antenna in order thus to be able to determine the magnitude and the phase provides that in addition to at least one transmitting antenna a reference antenna is also used, wherein this latter is disposed at a predetermined distance from the active antenna, and that additionally a signal generator is used which is connected to the at least one transmitting antenna and to the reference antenna and generates a transmission signal. Within the method, from the group of the following method steps:    ST1: only transmission of the transmission signal by the at least one transmitting antenna and capture of a power value of the transmission signal received by the active antenna;    ST2: only transmission of the transmission signal by the reference antenna and capture of a power value of the transmission signal received by the active antenna;    ST3: simultaneous transmission of the transmission signal by means of the at least one transmitting antenna and the reference antenna while generating superimposed transmission signals and capture of a power value of the superimposed transmission signals received by the active antenna;a sequence of at least three method steps ST1, ST2, ST3 is carried out in any order and in any combination, with at least one method step ST1, ST2, ST3 being carried out multiple times, wherein the sequence of the at least three method steps ST1, ST2, ST3 always comprises the method step ST3 at least once. Because the method step ST3 is carried out at least once, the phase can be determined with the aid of at least three measured power values. The required magnitude can be determined directly when ST1 is carried out or with the aid of the three measured power values, if ST1 is not carried out.
The measuring device for determining the power values of a signal received by an active antenna for calculation of the magnitude and phase comprises the features already mentioned. Such a measuring device also comprises a reference antenna in addition to at least one transmitting antenna, wherein the reference antenna, as already explained, is disposed at a fixed unchangeable distance and direction with respect to the active antenna. Moreover, the measuring device comprises a signal generator which can generate the transmission signal. In this case the signal generator is preferably connected both to the at least one transmitting antenna and also to the reference antenna. Furthermore, the measuring device has a control unit which is designed in such a way that it can carry out the following method steps:    ST1: only transmission of the transmission signal by the at least one transmitting antenna and capture of a power value of the transmission signal received by the active antenna;    ST2: only transmission of the transmission signal by the reference antenna and capture of a power value of the transmission signal received by the active antenna;    ST3: simultaneous transmission of the transmission signal by means of the at least one transmitting antenna and the reference antenna while generating superimposed transmission signals and capture of a power value of the superimposed transmission signals received by the active antenna.
Furthermore, the control unit is designed so that a sequence of at least three method steps ST1, ST2, ST3 is carried out in any order and in any combination, with at least one method step ST1, ST2, ST3 being carried out multiple times, wherein the sequence of the at least three method steps ST1, ST2, ST3 always comprises the method step ST3 at least once.
Furthermore, the method according to the invention and the measuring device according to the invention put the sequences in concrete terms in such a way that the corresponding following method steps are carried out in any order for each of the sequences a), b), c) described by way of example. The method step ST1 or ST2 is carried out within the sequence a). The method ST3 is also carried out which is repeated as often as required until at least three power values are captured. The method steps ST1, ST2 and ST3 are carried out within the sequence b). In the sequence c) the method step ST3 is carried out as often as required until at least three power values are captured. These sequences a), b), c) with their respective method steps enable the calculation of power values, with which the required magnitude and the required phase can be determined in a very simple manner.
The method according to the invention and the measuring device according to the invention describe the sequences a), b) and c) in greater detail below. Moreover, in the sequence a) a phase controller and/or amplitude controller is advantageously also used, or the measuring device advantageously also has such a phase controller and/or amplitude controller. After the method step ST3 has been carried out, a phase change is carried out between the transmission signal on the at least one transmitting antenna and the transmission signal on the reference antenna and/or an amplitude change of the transmission signal on the at least one transmitting antenna and/or of the transmission signal on the reference antenna is carried out. After this the method steps ST3 and the phase change and/or amplitude change are carried out again until at least one power value in each case is captured for at least two different phase values between the transmission signal on the at least one transmitting antenna and the transmission signal on the reference antenna and/or for at least two different amplitude values of the transmission signal on the at least one transmitting antenna and/or of the transmission signal on the reference antenna. Thus with the captured power values from the method step ST1 or ST2 three power values are provided. By means of the at least three power values it is possible to calculate the phase difference on the active antenna between the transmission signal which was transmitted by the at least one transmitting antenna and the transmission signal which was transmitted by the reference antenna. The magnitude of the transmission signal which was transmitted by the at least one transmitting antenna and was received by the active antenna can also be easily determined. This signal is either taken directly from the measured power value from the method step ST1, if this was carried out, or it is calculated from the at least three power values, of which at least two have been determined from the superimposed transmission signal.
Within the sequence b) it is only made clear that the phase is calculated from the at least three power values and that the magnitude is determined from the measured output in the method step ST1.
Likewise, in the sequence c) a phase controller and/or amplitude controller is advantageously used, or the measuring device advantageously also has such a phase controller and/or amplitude controller. After the method step ST3 has been carried out, a phase change is carried out between the transmission signal on the at least one transmitting antenna and the transmission signal on the reference antenna and/or an amplitude change of the transmission signal on the at least one transmitting antenna and/or of the transmission signal on the reference antenna is carried out. After this the method steps ST3 and the phase change and/or amplitude change are carried out again until at least one power value in each case is captured for at least two different phase values between the transmission signal on the at least one transmitting antenna and the transmission signal on the reference antenna and/or for at least three different amplitude values of the transmission signal on the at least one transmitting antenna and/or of the transmission signal on the reference antenna. The required phase and the required magnitude are determined by means of the at least three power values.
Moreover, an advantage according to the invention is provided when in the method and in the measuring device the capture of the power and the phase change and/or amplitude change are carried out one after the other as often as required until at least one power value in each case is captured for at least three or at least four different phase values between the transmission signal on the at least one transmitting antenna and the transmission signal on the reference antenna and/or for at least three different amplitude values of the transmission signal on the at least one transmitting antenna and/or of the transmission signal on the reference antenna. This enables a reliable determination of the phase also in the event that the amplitude of the two transmission signals has a markedly different level.
Moreover, it is particularly advantageous if the method and the measuring device are capable of turning and/or moving a unit which is formed by the active antenna and the reference antenna jointly relative to the at least one transmitting antenna. In this case different reception directions, that is to say different solid angles, can be measured. It is important that the reference antenna and the active antenna do not rotate and/or move with respect to one another. Furthermore the method and the measuring device can repeat the previous method steps, so that the magnitude and the phase can be determined for a different solid angle. In this case it is particularly advantageous if both the azimuth angle and also the angle of elevation of the unit formed by the active antenna and the reference antenna are turned and/or moved relative to the at least one transmitting antenna. In this case all solid angles of the active antenna can be measured. The active antenna can therefore be swiveled in two axes of rotation.
The method and the measuring device are then capable of rotating the active antenna together with the reference antenna until the magnitude and the phase have been determined for all solid angles or until the magnitude and the phase have been determined only for the required solid angles.
Both for the measuring device and also for the method it is particularly advantageous if four successive phase changes of 0°, Δ°, 2·Δ° and 3·Δ°, wherein Δ° is in the range between 80° and 100° and preferably corresponds to 90°, are applied between the transmission signal of the at least one transmitting antenna and the transmission signal on the reference antenna. An application of a further phase difference of 90° in each case can be achieved particularly simply by means of hybrids, inverters or selector switches. In this case care should be taken to ensure that, depending upon the length of the cables which are used from the RF generator to the at least one transmitting antenna and to the reference antenna, already from the outset there is a phase shift between the two transmission signals exists. Therefore the phase controller does not set a phase shift of for example exactly 90° between the transmission signal of the at least one transmitting antenna and the transmission signal of the reference antenna at the location of the active antenna, but only increases a possibly existing phase offset by a further 90°.
Moreover there is an advantage if within the method and within the measuring device an amplitude controller is used which is connected between the signal generator and the at least one transmitting antenna and/or between the signal generator and the reference antenna. By means of the amplitude controller it is possible to set the amplitude of the transmission signal on the at least one transmitting antenna and/or the amplitude of the transmission signal on the reference antenna in such a way that the power of the transmission signal of the at least one transmitting antenna corresponds approximately to the power of the transmission signal of the reference antenna on the active antenna. Therefore the power levels of both transmission signals on the active antenna are preferably the same. However, it is sufficient if the power of a transmission signal is less than 20 times as high, preferably less than ten times as high, or more preferably less than five times as high, or more preferably less than twice as high, as the power of the other transmission signal. In this case the phase for a solid angle can be calculated particularly accurately.
Furthermore in the method according to the invention and in the measuring device according to the invention it is advantageous if the at least one transmitting antenna and/or the reference antenna transmit a modulated or unmodulated transmission signal. This also makes it possible to measure active antennas which only operate with modulates signals.
Ultimately in the method according to the invention and in the measuring device according to the invention it is advantageous if the reference antenna is disposed particularly close to the active antenna, the distance between them being in particular less than 100 cm, preferably less than 50 cm, more preferably less than 25 cm and more preferably less than 10 cm.